7. Heat stress

The guidance is mainly for workplaces where heat stress is an issue all year, such as bakeries and foundries.

It will also help employers protect workers in very hot weather where there may be an increased risk.

What is heat stress?

Heat stress happens when the body's way of controlling its internal temperature starts to fail. As well as air temperature, factors such as work rate, humidity and work clothing may lead to heat stress.

You and your workers must be aware of how to work safely in high temperatures. This means identifying the factors that can cause heat stress, and how to avoid it.

A typical heat stress situation

Someone wearing protective clothing and doing heavy work in hot and humid conditions could be at risk because:

  • sweating is restricted by clothing and humidity
  • body heat increases due to work rate and, so core body temperature rises
  • the body reacts by producing more sweat, which may cause dehydration
  • heart rate also increases, putting more strain on the body

Symptoms of heat stress

Heat stress can affect people in different ways, and some are more likely to suffer it than others.

Typical symptoms are:

  • an inability to concentrate
  • muscle cramps
  • heat rash
  • severe thirst – a late symptom of heat stress
  • fainting
  • heat exhaustion – fatigue, dizziness, nausea, headache, moist skin
  • heat stroke – hot dry skin, confusion, convulsions and eventual loss of consciousness. This can result in death if not detected at an early stage

Where does heat stress occur?

Examples of workplaces where people might suffer from heat stress due to hot environments created by the process, or restricted spaces, are:

  • glass and rubber manufacturing plants
  • compressed-air tunnels
  • power plants
  • foundries and smelting operations
  • brick-firing and ceramics plants
  • boiler rooms
  • bakeries and catering kitchens
  • laundries

People adapt to hot conditions by cooling down through removing clothing, having cool drinks, using the shade or reducing work rate. However, in many work situations such changes may not be possible, for example during asbestos removal.

How do I assess the risks?

Where there is a possibility of heat stress occurring, you must assess the risks to workers. You need to consider:

  • work rate – the harder someone works the more body heat generated
  • working climate – this includes air temperature, humidity, air movement and working near a heat source
  • work clothing and personal protective equipment (PPE) – these may prevent sweating and other ways of regulating temperature
  • a worker's age, body type and medical factors (eg a hormonal imbalance) may affect their tolerance of heat

Firstly, talk to your workers (and their safety representatives) to see if they are suffering early signs of heat stress. If there is a problem, you may need expert advice from occupational health professionals.

We have a heat stress checklist to help you control the risks.

How can I reduce the risks?

Remove or reduce the sources of heat where possible.

Control the temperature

Control the temperature using engineering solutions, for example:

  • change the processes
  • use fans or air conditioning
  • use physical barriers to reduce exposure to radiant heat, for example machinery

Limit work rate and length of exposure

Provide mechanical aids where possible to reduce the work rate.

Regulate the length of exposure to hot environments by:

  • only allowing workers to enter the workplace when the temperature is below a set level or at cooler times of the day
  • issuing permits to work that specify how long people should work in situations where there is a risk
  • providing periodic rest breaks and rest facilities in cooler conditions

Prevent dehydration

Working in the heat causes sweating which means losing vital water that must be replaced. Provide cool water in the workplace and encourage workers to drink it frequently and in small amounts.

If it is not possible to drink while working, for example during asbestos removal, encourage workers to drink before and after the work to avoid dehydration.

We have more advice on preventing dehydration at work.

Personal protective equipment (PPE)

Protective clothing or equipment may expose the employee to heat stress.

Specialised personal protective clothing is available which incorporates, for example, personal cooling systems or breathable fabrics.

This may help protect workers in certain hot environments.

You can find more advice on PPE and working at high temperatures.


Provide training for your workers, especially if they are new or young. Tell them about:

  • risks of heat stress in their work
  • what symptoms to look out for
  • safe working practices
  • emergency procedures


Allow workers to acclimatise to their environment and identify which ones are assessed as fit to work in hot conditions.

Identify who is at risk

Identify workers who are more susceptible to heat stress. This could be due to inexperience, medication or a condition making them more vulnerable to heat stress, eg heart disease.

You may need advice from an occupational health professional or medical practitioner.

Your risk assessment should already address risks to pregnant workers. However, you may choose to review it when a worker tells you they are pregnant, to help you decide if you need to do any more to control the risks.

Monitor health

Where a residual risk remains despite your control measures, you may need to monitor the health of workers exposed to the risk.

You should seek advice from occupational health professionals experienced in the risks associated with heat stress.

Is this page useful?